Optical waveguides interconnect optical information processing devices, or connect such devices with other optical communication links such as glass optical fibers. Waveguides may be used to create passive optical devices such as splitters, combiners, couplers, routers and the like. In commonly used planar applications, waveguides are densely packed on substrates.
An optical waveguide typically comprises a transparent core that is capable of directing light signals therethrough, and a cladding comprising a material that affords a lower refractive index than the core material. Waveguides may be constructed as single monolithic structures lithographically provided on a substrate, or may comprise optical fibers.
In the electronics and optical fabrication technologies, optical interconnects have been used in backplane interconnections, board-to-board interconnections, clock distribution, and a variety of other applications. In particular, lithographic processes have been used because such processes are generally suitable for mass production.
The integration of polymeric materials in optics is an increasingly attractive alternative in devices such as switches, optical interconnects, splitters, and surface relief structures. As demand for band width and low cost integration has increased, polymers provide flexibility, high transparency and versatility in structure, and properties. In particular, fluoropolymers represent alternatives to current optical polymers due to their properties, such as low transmission loss (at 1300 and 1550 nm), low birefringence, good optical stability after thermal aging, and low moisture absorption. For example, fluoroacrylates developed by Allied Signal and others, Dupont's Teflon™ AF (tetrafluoroethylene and perfluorovinyl ether copolymer), Amoco's Ultradel™ (fluorinated polyimide) and Asahi's CYTOP™ (perfluorovinyl ether cyclopolymer) are fluoroplastics currently pursued for optical device manufacture. See, for example, Eldad, L; Schacklette, L. “Advances in Polymer Integrated Optics,” IEEE J. Quantum Electronics 2000, 6(1), 54.
The use of a perfluorocyclobutyl-based homopolymer in an optical waveguide has been disclosed. See Fishbeck, G.: Moosbuerger, R.; Kostrzews, C.; Achen, A.; Petermann, K. Electronic Letters 1997, 33(6), 518. Also, the use of various perfluorocyclobutane (PFCB) homopolymers has been disclosed for various electronics and other applications. See for example, U.S. Pat. No. 5,159,038; U.S. Pat. No.5,037,917 and related patents.
Several patents relate to optical devices and methods for constructing them. For example, U.S. Pat. No. 5,850,498 is directed to low stress optical waveguides. U.S. Pat. No. 6,210,867 B1 is directed to methods for fabricating low loss optical devices using a photoresist coated on a linear optical layer by a spin coating method. The photoresist is dipped into a developer fluid and baked, thereby forming a photoresist pattern defining specific areas upon which a metal layer is deposited. A vacuum deposition method such as sputtering, electron beam or thermal evaporation may be employed to deposit a metal substrate.
A pending U.S. patent application (U.S. Ser. No. 09/604,748) which is commonly owned by the assignee of the present application, discloses optical fluropolymers and methods of applying fluoropolymers in molding processes. The application is directed to the use of alternating perfluorocyclobutane and aryl ether linkages that are adapted for micromolding polymeric films by replicating a pattern or image directly from a silicon master.
In the case of forming a polymer film using spin coating techniques, it is necessary to form a coating of sufficient thickness to manufacture a waveguide. Many polymers cannot be dissolved at solids content when spin coated to manufacture a suitable waveguide thickness. In many instances, it requires multiple coats of polymer to achieve the necessary thickness, which introduces added interface problems, and can be costly and time consuming.
It has been recognized in the industry that a need exists for a suitable polymeric material and process that affords appropriate optical properties when applied in an optical device. A polymer and process of applying the polymer that is capable of achieving a suitably thick coating on the device is needed. A polymeric composition that is capable of maintaining a suitable solids thickness in solvent, thereby affording a relatively thick coating, is desirable. A composition and method of application that employs a minimum amount of solvent, and a maximum solids content, is needed. Furthermore, polymeric compositions that exhibits low loss in the telecommunications wavelength and a compositionally controlled refractive index to match that of the silica optical fibers and other components would be desirable.